1. Field of the Invention
The present invention relates to a flame retarding resin composition containing organo-phosphorus compound as a flame retarding agent, having high impact resistance, excellent heat resistance, and a superior self-fire-extinguishing characteristic.
2. Description of the Background Art
Conventionally, thermoplastic resins of which the impact resistance have been promoted by a rubbery polymer are known as resins generally called ABS resins. Such thermoplastic resins must have flame retardancy depending on use to which they are directed. This is particularly applicable when thermoplastic resins are used for household products, electrical appliances, OA equipment, automotive products, and building materials. A commonly known method of imparting flame retardancy to thermoplastic resins, such as ABS resins, consists of blending a flame retarding agent. In many cases, flame retarding agents comprise a halogen-containing compound such as a brominated diphenyl oxide compound, a brominated polycarbonate compound, or the like. A superior flame retarding effect is demonstrated when these flame retarding agents are blended together with antimony trioxide. However, the addition of said halogen-containing compound to resin compositions causes generation of noxious compounds, when the resin compositions are molded or burnt. In particular, generation of dioxin and furan which are fatally poisonous to human causes a serious problem.
As a solution to this type of problem, the addition of a compound containing phosphorus and/or nitrogen to the rubber-reinforced thermoplastic resin material, including ABS resins, as a flame retarding agent in place of a halogen-containing compound has been proposed. These compounds, however, are less effective in the flame-retarding effect than halogen-containing compounds. In addition, the flame-retarding effect of these compounds is especially low when they are used for styrene-type rubber-reinforced thermoplastic resins, such as ABS resin, so that a large amount of these compounds must be added in order to achieve an adequate flame-retarding effect. The addition of a large amount of the compounds containing phosphorus and/or nitrogen, however, conspicuously impairs impact resistance and heat resistance of the resin.
In an effort in eliminating this drawback, German Patent 3,401,835 A proposed a blend of a thermoplastic graft copolymer, a char-forming novolac resin, a phosphorus compound, and a melamine, as a polymer composition having a high flame retardancy. This polymer composition, however, produces melamine particles oozing from the resin, resulting in "blooming", by which the plastic surface is covered with deposited crystals. In addition, the use of phosphorus compounds which exhibit a plasticizing effect, remarkably impairs the heat resistance. Reducing the amount of phosphorus compounds improves the heat resistance, but does not provide a sufficient flame retarding effect. Therefore, development of a polymer composition exhibiting a high flame retarding effect without impairing impact resistance, heat resistance, and the like inherently possessed by plastics has been desired.
The present inventors have undertaken extensive studies in order to solve the above-mentioned problems and found that a flame retarding resin composition having high impact resistance, excellent heat resistance, and a superior self-fire-extinguishing characteristic can be obtained by a suitable combination of polymer blends having a specific composition.